NZ Transport Agency

Case study .

Is it safe to place street lighting behind wire rope barriers?

Sometimes the reality of running a road network doesn’t match the theoretical world of test standards and regulatory ideals. Different providers have different needs, which can result in compromises. The New Zealand Transport Agency were asked to optimise space on New Zealand’s road network and they came to us.

The questions:

What happens when you put a street light too close to a wire rope safety barrier and a vehicle hits the barrier? Will the occupants still be safe? Will the barrier still work properly? What happens to the street light?

We found the severity of the situation by creating a non-linear large displacement simulation model. Various sub-components of the model were calibrated against actual crash test data helping improve the simulation’s accuracy. We did a range of simulations for two vehicle types; a Toyota Starlet and a Chevrolet C2500 Pickup. We placed the lighting column in different offsets behind the barrier and various positions up and downstream from the impact point.

After complicated statistical analysis, results were compared against the requirements of NCHRP-350 and EN 1317-2 for effect on occupant safety. The findings showed occupant safety can be maintained even though the interaction between the street light and barrier significantly changes the barrier performance and vehicle behaviour. This finding allowed NZTA to maximise space and opt for non-standard street lighting installations while maintaining public safety.

Did you know?

  • The energy released when a vehicle impacts a road barrier is proportional to the square of the vehicle speed. As the add on TV says, the faster you go the bigger the mess.
  • An 8000 kg truck impacting a barrier at an angle of 15 degrees with an impact speed of 80 km/hr has less impact energy than a 2270 kg vehicle impacting the barrier at 20 degrees with a speed of 100 km/h.

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